Heretofore, styrenic polymers produced by the radical polymerization method have been molded to various shapes by various molding methods and widely used as domestic electrical appliances, office machines, household goods, packaging containers, toys, furnitures, synthetic papers and other industrial materials. Because of their atactic configuration in stereochemical structure, however, such styrenic polymers have suffered the disadvantages of inferior heat resistance and chemical resistance.
In order to solve the above-mentioned disadvantages of the styrenic polymers having atactic configuration, the group of the present inventors succeeded in the development of the styrenic polymers having a high degree of syndiotactic configuration, and further the styrenic copolymers of a styrene monomer and other comonomer (refer to Japanese Patent Application Laid-Open Nos. 104818/1987, 187708/1987 and 241009/1988).
These developed styrenic polymers or copolymers each having syndiotactic configuration are excellent in heat resistance, chemical resistance and electrical properties and are expected to find application use in a variety of fields.
The above-mentioned polymer, especially the syndiotactic polystyrene has a glass transition temperature in the range of 90.degree. to 100.degree. C. and a melting point in the range of 250.degree. to 275.degree. C.
Although the heat distortion temperature of the syndiotactic polystyrene at a low load is as high as the aforementioned melting point, that at a high load is about the aforesaid glass transition temperature, that is, almost the same as the heat distortion temperature of the conventional general-purpose polystyrene (GPPS), restricting the application of above-mentioned syndiotactic polystyrene along with the unsatisfactory toughness and elongation thereof.
In order to improve the properties of the styrenic polymer having syndiotactic configuration there has been proposed a syndiotactic polystyrene compounded with other thermoplastic resin such as a general-purpose resin including polyolefin, an engineering plastic typified by polyamide and polycarbonate, etc. or an inorganic filler. However, there has been still some room for further improvement on the aforesaid syndiotactic polystyrene with respect to the interfacial adhesivity and compatibility and the poor compatibility with other resin as mentioned above has limited the improvement on the properties of such syndiotactic polystyrene.
In order to improve the compatibility of the above-mentioned syndiotactic polystyrene there has been developed as a compatibilyzing agent a polymer produced by modifying an atactic polystyrene with an unsaturated carboxylic acid (refer to Japanese Patent Application Laid-Open No. 219843/1990), a styrenic copolymer produced by copolymerization with a vinylic compound having an epoxy group, a styrenic copolymer produced by copolymerization with an .alpha.,.beta.-unsaturated carboxylic acid anhydride (refer to Japanese Patent Application Laid-Open No. 209938/1990), and the like. However, the use of the polymer as mentioned above as a compatibilizing agent-has caused the problem of deteriorating the crystallizability of the composition which contains the above compatibilizing agent.
In addition, there has been known a styrenic copolymer comprising a styrenic repeating unit and maleimide repeating unit, in which the stereoregularity of the main chain of the styrenic repeating unit is mainly of syndiotactic configuration (refer to Japanese Patent Application Laid-Open No. 258805/1990). However, the aforementioned copolymer is insufficient in compatibility with the engineering plastics such as polyamide.
Under such circumstances there has been proposed a styrenic copolymer of styrenic repeating unit having syndiotactic configuration and a carboxylic acid or ester thereof for the purpose of improving the interfacial wettability with an inorganic filler while maintaining the heat resistance and chemical resistance of the foregoing polymers (refer to International Patent Application Laid-Open No. 78168/1989).
However, further improvement is desired for the above-proposed copolymer with regard to the interfacial adhesivity.